A composite X-ray (blue), radio (pink and green), and optical (orange and yellow) image of the galaxy Centaurus A presents a stunning tableau of a galaxy in turmoil. A broad band of dust and cold gas is bisected
at an angle by opposing jets of high-energy particles
blasting away from the supermassive black hole in the
nucleus. Two large arcs of X-ray emitting hot gas were
discovered in the outskirts of the galaxy on a plane
perpendicular to the jets.

The arcs of multimillion degree gas appear to be part
of a projected ring 25,000 light years in diameter. The
size and location of the ring indicate that it may have
been produced in a titanic explosion that occurred
about ten million years ago.

Such an explosion would have produced the high-energy
jets, and a galaxy-sized shock wave moving outward at
speeds of a million miles per hour. The age of 10
million years for the outburst is consistent with
optical and infrared observations that indicate that
the rate of star formation in the galaxy increased
dramatically at about that time.

Scientists have suggested that all this activity may
have begun with the merger of a small spiral galaxy and
Centaurus A about 100 million years ago. Such a merger
could eventually trigger both the burst of star
formation and the violent activity in the nucleus of
the galaxy. The tremendous energy released when a
galaxy becomes "active" can have a profound influence
on the subsequent evolution of the galaxy and its
neighbors. The mass of the central black hole can
increase, the gas reservoir for the next generation of
stars can be expelled, and the space between the
galaxies can be enriched with heavier elements.